So I had an external 3.5" drive that i backed up on 2 times...I then acquired a 2.5" palm sized drive to use w/ my laptop which is 80gb. My internal drive is also 80gb but has about 30 gb free. When i plug in this external FW drive and try to use time machine I get the errors that are attached in the pictures... I don't see how the backup can require 117.7 gb if I am trying to start over from scratch on the backup process. Is there a preference list I can delete to reset time machine to be as though I'd never used it before? Anyone have ideas what i can try? thanks.